Hair damage is characterized by dull looking, brittle fibers which tend to break easily and have increased porosity. In addition, cuticle cells tend to be uplifted indicating hair shaft damage with the presence of split ends.
The damage is caused by three types of insult: mechanical, chemical and environmental. Too frequent or excessive brushing or combing causes shaft damage, split ends and uplifted cuticle cells. Over-vigorous chemical treatments from perming, dying, bleaching or too alkaline shampoos cause hair protein hydrolysis and oxidation of cystine linkages. Environmental insult or hair “weathering” from climatic exposure, sunlight, air pollutants, wind, seawater and chlorinated swimming pool water cause photo oxidative splitting of cystine linkages, initiate free radicals detrimental to the protein matrix and increase porosity of the cuticle.
To better understand the extent to which hair has been damaged by such factors or treatments, or to evaluate the extent to which hair damage has been repaired by ameliorative procedures, objective measurements of hair properties are preferably made. These measurements have been mechanical such as, for example, measuring the hair's resistance to breakage, or they have been chemical in nature such as, for example, measuring the hair's solubility in selected media. Such measurements often require an extensive amount of time and/or a large amount of hair to complete. Further, these measurements may require specific instrumentation only found in specialized laboratories and, thus, are not capable of being conducted at or near a point of hair treatment.
Others have tried to evaluate hair damage using absorption of copper by hair. In these efforts, hair damage was indirectly determined by analyzing the amount of metal remaining in a treatment solution after the solution was exposed to a hair sample. By determining the amount of metal remaining in the solution, an inference was made as to how much metal was absorbed by the hair. This amount of metal was presumed to be related to the amount of hair damage. Unfortunately, such indirect measurements may not have the accuracy and precision required to differentiate the amount of damage in closely related hair samples. Moreover, such indirect measurements may be complicated by contamination: that is, contributions to the solution's metal content by metal already present in the hair may skew the results, particularly when more commonly occurring metals such as copper are used. Finally, such indirect measurements may not be accurate owing to the loss of metal ions to other locations such as, for example, the containers used for the treatment process, thereby skewing the results.
For example, previous work by Tripathi and Tomaszewicz (1981) describes the use of a copper solution to evaluate hair damage and the indirect measurement of the residual copper solution to determine the amount of copper uptake. This indirect measurement was conducted using a laboratory-based titration. A similar approach is described by Kabacoff and Govil (1985) and by Kabacoff et al. (1987) which use copper absorption by hair and the indirect measurement of the resulting copper solution. In these efforts, the copper concentration is determined by measuring the color intensity of the resulting solution. The color intensity is compared to a physical color standard (color chart, color tube or glass slides), thereby requiring a subjective evaluation. More objective measurements of the color intensity, such as a filter photometer or an impedance measurement, can also be performed. However, such measurements do not result in an objective determination of the actual amount of metal present, only the evaluation of the color of the solution.
Furthermore, existing methods of hair damage evaluation are typically not sensitive enough to provide reliable results for damage to hair resulting from all kinds of hair treatments, particularly in view of the fact that cosmetic companies have been developing gentler hair products which, when used, inflict less damage to hair than the previous generation of products.
Thus, there is a need in the art to have sensitive, direct, objective measurement procedures for determining the amount of damage to hair, procedures which are easy to employ, use a small amount of hair, require a short amount of time, and/or utilize uncomplicated equipment which allows the procedures to be practiced at or near a point of hair treatment (such as, for example, a beauty or hair salon).